A 190-kDa antigen is present around lipid droplets of rat pulmonary lipofibroblasts

By using a monoclonal antibody (mAb A2) raised against the cytoskeleton of goldfish xanthophores, we found that a 190-kDa protein is localized along t he rim of lipid droplets In rat pulmonary lipofibroblasts (lung septet cell s). By immunofluorescence microscopy of frozen sections, we observed mAb A2 bound to the rim of lipid droplets in the lipofibroblast in vivo. The circ ular labeling around lipid droplets as well as filamentous labeling in the cytoplasm was observed in lipofibroblasts in culture. In cells cultured for several days, the number and size of lipid droplets decreased and the circ ular labeling became indistinct, whereas the filamentous labeling persisted . In Western blotting, mAb A2 recognized 190-kDa and 58-kDa bands in the cu ltured lipofibroblast; the latter was found to be vimentin. Treatment of li pofibroblasts for 4 hr with Colcemid extinguished the labeling around lipid droplets, and only the coarse filaments that matched the anti-vimentin lab eling remained. Interestingly, after more than 12 hr of Colcemid treatment, the circular labeling reappeared around lipid droplets. The disappearance of the circular labeling also occurred when lipofibroblasts were treated wi th Taxol or cytochalasin B for more than 4 hr. From Western blotting, this mAb A2 appears to recognize a common epitope shared by vimentin and the 190 -kDa antigen. The result indicates that the 190-kDa protein recognized by m Ab A2 is localized around lipid droplets of lipofibroblasts and that this l ocalization may be related to the cytoskeleton.